doc: exclude dot dirs from Sphinx builds

It's handy to place e.g. a Python virtual environment in a .venv
subdirectory. The virtual environments contain .rst files, which cause
Sphinx warnings when Sphinx descends to them. Just exclude all dot dirs
from Sphinx builds.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>

conf.py

@@ -17,7 +17,7 @@ release = '1.0'
 extensions = []
 
 templates_path = ['_templates']
-exclude_patterns = ['_build', 'Thumbs.db', '.DS_Store', 'README.rst']
+exclude_patterns = ['_build', 'Thumbs.db', '.DS_Store', 'README.rst', '.*']
 
 root_doc = 'index'